"Get to sector 5 without upgrading your reactor in the Zoltan Cruiser."
To earn this achievement, the ship's reactor cannot be upgraded at all before it reaches the fifth sector. Systems and subsytems can be upgraded, but only Zoltan crew members can provide more power without invalidating a run.
Purchasing Cloaking would help your survival during early-game, as Leto Missiles combining with Halberd Beam would be sufficient for defeating most easier opponent. Power required to run the Cloaking System could be acquired by either powering down non-critical Systems like Medbay or Shield, or by hiring/rescuing Zoltan crews.
Someone trying to unlock Manpower can make a "pacifism run" and attempt to earn many of the "Going the Distance" achievements at the same time by just fleeing every battle as quickly as the FTL drive can charge. However, this would make it fairly difficult to beat the game in the same run.